1.Butterfat
Each fat globule is surrounded by a membrane consisting of phospholipids and proteins; these emulsifiers keep the individual globules from joining together into noticeable grains of butterfat and also protect the globules from the fat-digesting activity of enzymes found in the fluid portion of the milk. The fat-soluble vitamins A, D, E, and K are found within the milk fat portion of the milk.
2.Milk Proteins
Milk contains about 3.3% protein. Milk protein contains all the nine essential amino acids required by human beings. Milk protein is synthesized by the mammary gland, but 60% of the amino acids used to build the proteins are obtained from the cows diet. Total milk protein and amino acid composition varies with cows breed and individual animal genetics.
There are two major categories milk protein that are broadly defined by their chemical composition and physical properties. These are casein and whey protein.
Casein family contains phosphorous and will coagulate at pH 4.6. The serum (Whey) proteins do not contain phosphorous, and remains in solution in milk at pH 4.6.
The largest structures in the fluid portion of the milk are casein protein. Casein proteins make up around 80% of the protein in milk, by weight. Most of the casein proteins are bound into the micelles. In cow’s milk, approximately 82% of milk protein is casein and the remaining 18% is Serum, or Whey protein.
The high phosphate in casein family allows it to associate with calcium and form calcium phosphate salts. The abundance of phosphate allows milk to contain much more calcium, thus casein proteins provide good source of calcium for consumers.
The whey protein family consist approximately 50% beta lactoglobulin, 20% alpha lactoalbumin, blood serum albumin, immunoglobulin, lactoferrin and many minor protein and enzymes.
Wey protein do not contain phosphorous, but do contain a large amount of sulfur-containing amino acids. These forms disulfide bonds within the protein causing the casein to form a compact spherical shape. The disulfide bonds can be broken, leading loss of compact structure, a process called denaturation. Denaturation is an advantage in yoghurt production because it increases the amount of water that protein can bind, which improves the texture of yoghurt. Whey protein can also be used to bind water in meat and sausage production due to its denaturation factor.
The function of;
i. ß – Lactoglobulin is thought to be a carrier of vitamin A.
ii. a – lactoalbumin plays a critical role in the synthesis of lactose in the mammary gland.
iii. Immunoglobulins plays a role in the animals immune system
iv. Lactoferrin and transferrin play an important role in iron absorption
Influence of heat treatment on milk proteins
The casein is stable to heat treatment. Typically high temperature short time (HTST) pasteurization conditions will not affect the functional and nutritional properties of the casein protein. High temperature can cause the interaction between casein and whey proteins that affect the functional but not the nutritional properties e.g. at high temperature ß – Lactoglobulin can form a layer over the casein micelle that prevents curd formation in cheese.
The whey protein are more sensitive to heat than caseins. HTST pasteurization will not affect the functional and nutritional properties of whey proteins. Higher temperature treatments may cause denaturation of ß – Lactoglobulin, which is an advantage in the production of some foods. Severe heat treatment such as ultra high pasteurization may cause some damage to heat sensitive amino acids and slightly decrease the nutritional content of milk.
3.Milk Sugar
Milk contains approximately 4.9% carbohydrate. The carbohydrate lactose gives milk its sweet taste and contributes approximately 40% of whole cow's milk's calories. Lactose is a disaccharide composite of two simple sugars, glucose and galactose. In nature, lactose is found only in milk and a small number of plants.
Lactose physical properties
Lactose is dissolved in the serum (whey) phase of milk. Lactose dissolved in solution is found in two forms, called the a - anomer and ß – anomer, that can convert back and forth between each other. The solubility of the two anomers is temperature dependent and therefore the equilibrium concentration of the two forms will be different at different temperatures. At room temperature (20 degrees Celsius) the equilibrium ratio is approximated 37% a and 63% ß – Lactose. At temperatures 93 degrees Celsius the ß – anomer is less soluble so there is a higher ratio of a – to ß – lactose. The type of anomer present does not affect the nutritional properties of lactose.
Influence of heat on heat treatment on lactose properties
The normal pasteurization conditions used for fluid milk have no significant on lactose. The higher temperatures used for ultra high temperature (UHT) pasteurization of extended shelf life products and spray drying can cause browning and isomerization reactions, which may affect quality and nutritional properties. The browning reaction called the Mailllard reaction, occurs between the lactose and protein in milk and produces undesirable flavour and color and decreases the available content of the amino acid lysine in milk protein. The isomerization reaction is a molecular rearrangement of lactose to lactulose. Lactulose is produced for use by the pharmaceutical industry in pill production.
Lactose Intolerance
Lactose, the disaccharide sugar component of all milk must be cleaved in the small intestine by the enzyme lactase in order for its constituents (galactose and glucose) to be absorbed. The production of this enzyme declines significantly after weaning in all mammals. Consequently, many humans become unable to properly digest lactose as they mature. There is a great deal of variance, with some individuals reacting badly to even small amounts of lactose, some able to consume moderate quantities, and some able to consume large quantities of milk and other dairy products without problems. When an individual consumes milk without producing sufficient lactase, they may suffer diarrhea, intestinal gas, cramps and bloating, as the undigested lactose travels through the gastrointestinal tract and serves as nourishment for intestinal microflora who excrete gas, a process known as anaerobic respiration.
Lactose intolerance is a natural process and there is no reliable way to prevent or reverse it. Lactase is readily available in pill form, and many individuals can use it to briefly increase their tolerance for dairy products.
Titany answered the question on April 25, 2022 at 07:20